Performing a hard reset on your LG LS740 should always be the last resort to solve kinds of problems of your handset.
How to hard reset Spritn LG LS740 (LG F90)
In status of power off,press power button + volume down button and hold
Select ‘wipe data/factory reset’ and press power button
Select ‘Yes’ and press power button
Select ‘reboot system now’ and press power button
Now, Your device will be rebooted and You have it back to its factory default settings